The completion of oil and gas wells by gun perforating is well known in the art. A work string including one or more perforating guns is lowered into a well casing cemented into the wellbore. The perforating guns are positioned adjacent to the formation to be perforated. The perforating guns are fired to penetrate the casing and cement and form perforations into the producing formation for recovery of the desired fluids. These perforating guns typically utilize shaped charges to form the perforations.
Typically, a firing head is positioned at the top of the string of guns and is connected to the uppermost gun of a string of guns. A time domain firer (TDF) is positioned between adjacent pairs of guns. When the firing head is triggered, the uppermost gun is then fired, and the time domain firers then cause the string of guns to be fired sequentially from top to bottom. On occasion, the firing sequence is from bottom to top.
There is inherent risk in handling the explosive components which must be assembled to make a perforating gun. Even after the guns are assembled, there is risk in handling the completed guns. The assembled guns are typically connected to a drill string for placement in the borehole. Safety regulations increasingly discourage or prohibit the manual handling of perforating guns on drill rigs due the risks involved. As a result, there is a need for apparatus and methods which allow perforating guns to be handled automatically on drill rigs.